Bubbles having a diameter of 50 μm or less (microbubbles) are known to have properties different from those of normal bubbles, but the properties of the microbubbles have not yet been well understood. For that reason, various microbubble generators under development recently only generate microbubbles of a gas in aqueous solution, and there is almost no invention that makes the most of the potential properties of microbubbles. An example of the traditional technology using microbubbles is the method described in JP-A-2002-143885 of accelerating the biological activity, metabolism, and consequently growth of organisms. However, although the invention has significant advantages in the field of cultivation of fish and shellfish, it does not disclose or suggest anything about collapsing microbubbles.
An example of the technology using the collapsing phenomenon of bubbles is a method of irradiating an ultrasonic wave in aqueous solutions. However, the method is extremely low in efficiency because the bubbles for collapsing are generated by cavitational action of the ultrasonic wave itself, and has a problem of difficulty in commercialization because of its restricted functions. Since cavitation bubbles contain steam and are present only for an extremely limited period of microseconds, the method had problems that it was not possible to use the effect of another kind of gas as the main content and the effect of the electric charge formed at the gas-liquid interface of the bubbles.